drm/i915: Increase the range of sideband address.

Looks like latest BSW/CHV production system has sideband address > 128.
Use u32 data types to cover new offset/address range :)

Signed-off-by: Deepak S <deepak.s@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>